Apparatus for detecting inter-cylinder air-fuel ratio imbalance in multi-cylinder internal combustion engine

Abstract

An apparatus for detecting inter-cylinder air-fuel ratio imbalance in an engine is provided. The apparatus includes a turbocharger, a bypass passage configured to bypass a turbine of the turbocharger, a waste gate valve configured to selectively close the bypass passage, an air-fuel ratio sensor installed in a portion of an exhaust passage which portion is located on a downstream side of a junction between a downstream side of the turbine and a downstream side of the bypass passage, and a determination unit programmed to compare a value of a degree of fluctuation in an output from the air-fuel ratio sensor or a parameter correlated therewith with a predetermined threshold to perform inter-cylinder air-fuel ratio imbalance determination. The determination unit is programmed not to perform the imbalance determination when an opening degree of the waste gate valve is equal to or higher than a predetermined reference value.

Description

TECHNICAL FIELD[0001]The present invention relates to an apparatus for detecting imbalance (i.e. variation abnormality) of inter-cylinder air-fuel ratio of a multicylinder internal combustion engine, and in particular, to an apparatus that detects that the air-fuel ratio varies among cylinders relatively significantly in a multicylinder internal combustion engine.BACKGROUND ART[0002]In general, to efficiently remove harmful components of exhaust gas for purification using a catalyst, an internal combustion engine with an exhaust purification system utilizing the catalyst needs to control the mixing ratio between air and fuel in an air-fuel mixture combusted in the internal combustion engine, that is, the air-fuel ratio. For such control of the air-fuel ratio, an air-fuel ratio sensor is provided in an exhaust passage of the internal combustion engine to perform feedback control to make the detected air-fuel ratio equal to a predetermined target air-fuel ratio.[0003]On the other hand...

AI Technical Summary

Benefits of technology

The present invention is an inter-cylinder air-fuel ratio imbalance detection apparatus that improves detection accuracy and suppresses misdetection. It achieves this by programming a determination unit not to perform inter-cylinder air-fuel ratio imbalance determination when the opening degree of the waste gate valve is equal to or higher than a predetermined reference opening degree. This prevents a decrease in accuracy resulting from the mixture of exhaust gas having passed through the turbine and exhaust gas having passed through the bypass passage. Additionally, under normal control conditions where the waste gate valve is demanded to be opened, the invention controls the waste gate valve to close to a predetermined opening degree or less to suppress unintended degradation of drivability. Furthermore, the invention controls the multicylinder internal combustion engine and the automatic transmission to make the rotational speed lower and the load higher than those for the normal control to accurately determine the inter-cylinder air-fuel ratio imbalance. The invention also exerts an excellent effect that suppresses the adverse effect of the mixture of exhaust gas having passed through the turbine and the exhaust gas having passed through the bypass passage.

Problems solved by technology

Consequently, such a low-level variation would not affect exhaust emissions and pose an obvious problem.

However, if, for example, fuel injection systems for some cylinders become defective to significantly vary the air-fuel ratio among the cylinders, the exhaust emissions disadvantageously deteriorate.

Such a significant variation in air-fuel ratio as deteriorates the exhaust emissions is desirably detected as abnormality.

PTL 2 notes that, in a similar mechanical configuration, when the air-fuel ratio imbalance detection is performed while the waste gate valve is closed, the accuracy of the air-fuel ratio imbalance detection is deteriorated due to the adverse effect of stirring of exhaust gas by the turbine.

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